The activities of U.S. Department of Defense (DoD) and its contractors result in the generation of large amounts of hazardous wastes. Many of the constituents of concern are waterborne or have become waterborne as a result of leaks or spills. Among the most troublesome of these wastes are organic solvents, heavy metals, acids and salts. Even at low concentrations, these constituents are often toxic, tend to be resistant to conventional treatment methods and are persistent in the environment. Common waste constituents include the following:
Aromatic hydrocarbons PA1 Halogenated hydrocarbons PA1 Heavy metals PA1 Inorganic acids and salts PA1 "A culture medium of defined chemical composition . . . inoculated with a mixed population of microorganisms . . . and incubated under defined cultural conditions. Those microorganisms best adapted to the given environment . . . are selected (i.e., favored) and finally predominate. Conversely, those microorganisms poorly adapted to the conditions provided are counter-selected (i.e., disfavored) and either disappear or become a minority component of the mature enrichment culture." (Stolp H. and Starr, M. P. Principles of isolation, cultivation, and conservation of bacteria. In M. P. Starr, H. Stolp, H. G. Truper, A. Balows, and H. G. Schlegal (Eds.), The Prokarvotes (volume I) 948-977, New York: Springer-Verlag, 1981) While enrichment can be accomplished in a variety of ways, this invention primarily uses "kinetic control" of continuous cultures as an "open system" selection mechanism. With kinetic control, growth rate (dilution rate or mean cell residence time) is used to favor particular microorganisms and disfavor others. In general, it involves operation of serial continuous cultures at successively lower dilution rates. If cell recycle is practiced, the downstream reactor(s) are operated at a greater mean cell residence times (MCRT) than upstream reactor(s). This enrichment technique can be used to enrich in an upstream reactor microorganisms or consortia that are capable of more rapid growth than those enriched in a downstream reactor.
benzene PA2 toluene PA2 ethylbenzene PA2 xylenes PA2 phenols PA2 cresols PA2 tetrachloroethylene (PCE) PA2 trichloroethylene (TCE) PA2 1,1,1-trichloroethane (TCA)
Benzene, toluene and xylenes are components of fuels and often the focus of groundwater cleanup efforts. Phenols and cresols are used in paint stripping and carbon (smut) removal operations. Halogenated hydrocarbons are used as solvents and in vapor degreasing operations. Heavy metals, acids and inorganic salts are present in metal stripping and electroplating effluents.
In liquid wastewater streams, in sludges and in contaminated groundwater, the above constituents are often found together. It is appropriate, then, to seek remediation processes that handle mixed hazardous waste streams.